Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
A copying machine, a facsimile, a scanner or a similar device is an image reading apparatus that reads a document image with a line sensor. Typically, the line sensor includes imaging elements installed in one row in a main-scanning direction. After placing a document on an exposure glass, the line sensor moves in a sub-scanning direction to read an image. However, reading the document image while a foreign object such as dust adheres to the exposure glass causes its foreign object to be contained and read as the image. Therefore, one technique detects presence of the foreign object by which an imaging member reads a margin of the document and detects abnormalities in an image data.
There is a method for detecting the presence of the foreign object by a compared difference between white reference surface data which an imaging apparatus acquires by reading a white reference surface and the white reference data which is pre-stored in a non-volatile memory.
Another technique detects a noise line on the image, which the image data shows, in a short time from the start of document reading and performing a removal correction.